A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Is it ever legal to not install a MBJ in a CT cabinet? I looked at a 600A cabinet today and was told the MBJ was an option:?
CT Cabinet
- Thread starter A/A Fuel GTX
- Start date
- Status
TimK
Member
- Location
- Tacoma, WA
I have always "split" the ground, bonded incoming conduit, nipple to disconnect and then continued on into first means of disconnect. I don't believe I have seen the Neutral terminated inside the CT can itself.
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
So you install a rigid nipple from the CT cabinet to the first disconnect, install a bond bushing to the nipple and land the GEC to the bond bushing and then to the neutral bar in the disconnect? Is that what you are referring to the "split" ground? Meter sockets bond the neutral to the case, why not CT cabinets?
TimK
Member
- Location
- Tacoma, WA
Well, because under general conditions it is three phase and the meter does not need a neutral, if it did they (POCO) would take it off of the disconnect. It's not like you are going to measure or get credit for power that goes back on the neut.?
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
The two power companies we have here each want it done differently.
The first one(the way I like) lets you jump from the neutral buss in the CT can to the lug in the bottom of the can. Done, easy deal.
The second one doesn't want that jumper in the can. They want you to run a wire from the neutral buss in the service disconnect out of the panel and lug to the OUTSIDE of the CT can. Grind the paint, drill a hole, bolt a lug. Huge waste of time, looks like crap too.
And now the inspector is on a DB lug trip, he won't accept regular aluminum lugs outdoors. So now we either use DB lugs or crimps, which are easier to find in the larger sizes.
The first one(the way I like) lets you jump from the neutral buss in the CT can to the lug in the bottom of the can. Done, easy deal.
The second one doesn't want that jumper in the can. They want you to run a wire from the neutral buss in the service disconnect out of the panel and lug to the OUTSIDE of the CT can. Grind the paint, drill a hole, bolt a lug. Huge waste of time, looks like crap too.
And now the inspector is on a DB lug trip, he won't accept regular aluminum lugs outdoors. So now we either use DB lugs or crimps, which are easier to find in the larger sizes.
meternerd
Senior Member
- Location
- Athol, ID
- Occupation
- retired water & electric utility electrician, meter/relay tech
From a utility perspective....Code does not limit neutral grounds ahead of the service disconnect, but there must be a main bonding jumper at the service disconnect and none downstream. It's an AHJ issue whether or not to bond a neutral in the CT cabinet. Our utility does not allow bonding of the neutral anywhere but at the service disconnect. We tie the neutral to ground at our transformers, but nowhere else. The purpose of the MBJ is to provide a low impedance path to the neutral during a ground fault to trip the main breaker. Grounding ahead of the breaker really serves no purpose. Just my humble opinion....
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Down here, the Southern Company (Georgia Power, etc.) will not allow your grounds inside the CT cabinet, the engineers say they do their own grounding.
Your post has me confused. Just exactly what are you calling an MBJ?
The MBJ(s) always gets installed in the service disconnect enclosure(s).
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
OK....Maybe I have the terminology wrong, but I'm referring to a physical connection between the CT cabinet enclosure and the grounded conductor just like 200/320A meter sockets use.
Okay... drop "main".
250.80 requires the metal service enclosures and raceway be connected to the grounded system conductor (or grounding electrode conductor if an ungrounded system). Typically the direct, shortest jumper method is used. However, if metal raceway is used, doing so creates a parallel path for neutral current, thus the option to not directly bond [250.6]... and run a bonding jumper from the service disconnect enclosure... or use direct bonding and insert a non-conductive section of raceway (or fitting) between CT cabinet and service disconnect enclosure(s).
Last edited:
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Understood but in this case or that of any service, between the meter and the MDP, the parallel path is acceptable IMO, if a metallic raceway is used. PVC would be a better choice to eliminate that result but sometimes isn't spec'd.
The thing is, it is a violation of 250.6. ... "The grounding of ... conductive normally non?current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable currents".
Isolating the grounded neutral from the metal enclosure and raceway at the CT cabinet, and running a bonding jumper for the cabinet and raceways to the service disconnect eliminates the parallel path. IMO, this is a practicable method in all installations using metal enclosures and raceways.
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
Point well taken. I can't dispute what 250.6 states. So all the 200A services I've done that have a factory installed bonding jumper in the meter socket and are connected to the MDP via a 2" rigid nipple are illegal? Perhaps I should start removing the meter socket bonding jumper from now on or just use PVC exclusively as a raceway.
- Status